The conditions causing a shift in earthquake preparedness towards early warning systems primarily include:
A: lack of sufficient buy-in for retrofitting cities with earthquake-resistant buildings - This suggests that due to the challenges in implementing structural upgrades, the focus is shifting to early warning systems that can provide immediate alerts to individuals before shaking occurs.
While options B, C, and D touch on aspects that may influence earthquake preparedness, they don't specifically address the increased emphasis on early warning systems as directly as option A does.
In summary, A is the most relevant option explaining the shift towards early warning systems in earthquake preparedness.